Well, right now SBD comes from reward payouts, which is what automatically ramps up with the STEEM price, so if you got rid of STEEM reward payouts you could, and indeed would have to, completely change the mechanism surrounding how SBD gets created.

However, you can't in general place arbitrary controls over the supply of any stable coin, or it won't remain stable. You have to choose between stable price and unstable supply or stable supply and unstable price (or perhaps some point in the middle with nothing being actually stable, but just volatility-dampened).